<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <style>
    * {
      padding: 0;
      margin: 0;
    }
    .box {
      margin: auto;
      width: 1000px;
      height: 3000px;
      background-color: #cfa;
    }
    .tools {
      position: fixed;
      /* 浏览器的一半 */
      right: 50%;
      bottom: 30%;
      /* 版心的一半 + 调整 */
      margin-right: 550px;
      width: 50px;
      height: 320px;
      background-color: #666;
    }
  </style>
  <body>
    <div class="box"></div>
    <div class="tools"></div>
  </body>
</html>
